1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a method of inspecting a film on a semiconductor workpiece for residues.
2. Description of the Related Art
Inspection has been an integral component of semiconductor processing since the development of the earliest germanium-based bipolar integrated circuits. The need for inspection then and now stems from both engineering and economic considerations. Process engineers must be able to track the behavior of the multitude of individual process steps used to fabricate a given integrated circuit. From an economic standpoint, it is critical for semiconductor manufacturers to be able to quickly pinpoint the origin of unacceptable yields so that the circuit design or the fabrication process may be altered as necessary without needlessly wasting lots of wafers that may cost several hundred thousand dollars or more.
Morphology of VLSI and ULSI structures is generally determined by three microscopic techniques, namely, optical microscopy, scanning electron microscopy (xe2x80x9cSEMxe2x80x9d), and transmission electron microscopy (xe2x80x9cTEMxe2x80x9d). Optical microscopy is useful for studying wide field of use structures and structures that do not require magnification greater than about 1000xc3x97. SEM imaging involves the detection of secondary electrons emitted from a surface bombarded by a primary electron beam, and can yield information on line width, film thickness, step coverage, edge profiles after etch and other morphology data. SEM imaging has a maximum magnification value that is several orders of magnitude greater than the maximum magnification possible using optical microscopy. TEM imaging involves the production of an image due to the differential loss of electrons from an incident beam as it passes through a very thin film sample. The sample image must be thin enough to transmit the beam so that essential information caused by differences in sample thickness, phase composition and other irregularities is preserved. TEM imaging, while limited to particular film thicknesses, has a larger maximum magnification value than SEM imaging.
Various types of surface anomalies have proven difficult to detect using the aforementioned optical, SEM and TEM techniques. For example, residual oxide films an underlying nitride films have been historically difficult to see using optically microscopy. The problem stems from the behavior of light reflected from the oxide residue and the underlying nitride film. If the incident illuminating light is normal to the films, light reflected from the oxide film may not be differentiated from light reflected from the nitride film. If the incident light is protected at a low angle relative to the plane of the films, surface topography may prevent differentiation of light reflected by the oxide versus the nitride films. While SEM techniques are not prone to the light reflecting issues, structures with irregular topography, such as high aspect ratio trenches, may be not adequately imaged with SEM. As to TEM imaging techniques, relatively thick films may not be adequately imaged for residue detection purposes.
The problem of residue detection is not confined to residual oxide on nitride films. There are numerous situations in modern semiconductor processing where residual films may adversely impact device performance or yield. Residual resist on polysilicon structures and residual silicon oxynitride anti-reflective coating on metal layers represent just two such examples.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a method of inspecting a film on a semiconductor workpiece wherein the film has a known infrared signature is provided. The method includes heating the workpiece so that the film emits infrared radiation and sensing the infrared radiation emitted from the film. The infrared signature of the radiation emitted from the film is compared with the known infrared signature and a signal indicative of a deviation between the infrared signature of the emitted infrared radiation and the known infrared signature is generated.
In accordance with another aspect of the present invention, a method of inspecting a film on a semiconductor workpiece wherein the film has a known infrared signature is provided. The method includes heating the workpiece so that the film emits infrared radiation and sensing the infrared radiation emitted from the film with an infrared camera that has a field of view defined by a plurality of pixels and is operable to sense an infrared signature corresponding to each pixel. The infrared signature of the radiation emitted from the film at each pixel is compared with the known infrared signature and a signal indicative of a deviation between the infrared signature of the emitted infrared radiation at each pixel and the known infrared signature is generated.
In accordance with another aspect of the present invention, a method of inspecting a silicon nitride film for the presence of residual oxide wherein the silicon nitride film has a known infrared signature is provided. The method includes heating the workpiece so that the silicon nitride film emits infrared radiation and sensing the infrared radiation emitted from the silicon nitride film. The infrared signature of the radiation emitted from the silicon nitride film is compared with the known infrared signature of the silicon nitride film and a signal indicative of a deviation between the infrared signature of the radiation emitted from the silicon nitride film and the known infrared signature is generated.